A power conversion system that operates a plurality of alternating current rotating machines with a plurality of inverter devices (power conversion devices) can generally be structured as a system including a master device, which forms a top level control device of the system, for commanding an alternating current rotating machine rotation speed, or the like, as a target value, or for carrying out monitoring or the like. This kind of power conversion system for driving alternating current rotating machines is such that, by the system being structured as an information link system wherein the inverter devices of the plurality of alternating current rotating machines are connected by a communication line utilizing optical communication, or the like, appropriate control is possible before an alternating current rotating machine fails, based on the temperature of the alternating current rotating machine and current information detected by the inverter devices.
FIG. 6 is a system configuration diagram showing one example of a heretofore known power conversion system.
The power conversion system realizes a synchronous operation, a ratio operation, and a start/stop control of a plurality of alternating current rotating machines M1 to M3 using a top level control device 10. Herein, a PLC (Programmable Logic Controller) or a personal computer is used as a master station. Also, a plurality of power conversion devices 11 to 13, having the same function, for driving the alternating current rotating machines M1 to M3 respectively are connected as slave devices to the top level control device 10 using one communication line 21.
Herein, for example, optical fiber or the like is used for the communication line 21, and each of the power conversion devices 11 to 13 is connected to the top level control device 10 via a bidirectional module. Also, accompanying instruments such as a temperature sensor 14 and a pressure sensor 15 are also connected as slave stations, and it is thus possible to provide necessary information to the top level control device 10 via the communication line 21.
The heretofore known power conversion system is such that the top level control device 10 centrally controls information from each of the power conversion devices 11 to 13, and accompanying instruments such as the temperature sensor 14, via the communication line 21, and issues various kinds of command, such as a start/stop command or speed command, to the plurality of power conversion devices 11 to 13, which are slave devices, while determining the status of each one. Consequently, in the event that there occurs a disconnection of the communication line 21 connecting the power conversion devices 11 to 13, it is necessary for the top level control device 10 to carry out a protective operation stopping the output of the top level control device 10, or the like. Because of this, in the event that communication from the master station becomes impossible for a reason such as a disconnection of the communication line 21 connecting the master station and slave stations or a failure of a communication control instrument, automatic recovery is not possible, and the system lacks stability.
Also, there is also a case wherein an operation command or speed command to the power conversion devices 11 to 13 does not pass through the communication line, but is transmitted by an operation command using a digital on/off signal from the exterior, or a speed command, or the like, based on an analog voltage (current) input command from the exterior. In this kind of case too, it is necessary to share information for predictive maintenance, and the like, based on temperature and inverter current information before a machine fails.
As another power conversion system, there is proposed a system wherein, in an inverter configured of a power unit formed of a power source unit and a power conversion unit, a control unit formed of an application unit that can be customized by linking with parameters a combination of a plurality of execution code function blocks installed in advance, an execution code unit formed of a motor control unit, and a CPU (Central Processing Unit) that executes an execution code, and an interface unit for communication with the exterior, the inputs and outputs of a plurality of inverter devices having the same function are connected by communication, and each inverter device is assigned as a master station or slave station (refer to Patent Document 1).
Herein, one of the plurality of inverter devices having the same function becomes the master station, and a transmission and reception of write data or read data is carried out with the remaining inverter devices. Consequently, a small-scale system can be realized without using a high-cost PLC or communication control option card.